Are you looking to do this because you are having overheating issues? If your fan(s) are coming on at 230 degrees and the temp lower as they should I'd say if it's not broke don't fix it.
Cooling my C4 1996 LT4
Thread Starter
Intermediate
Joined: Aug 2025
Posts: 32
Likes: 8
From: Wilsonville, Oregon
Cooling my C4 1996 LT4
I’ve read a lot but nothing that’s easy to follow. I either want to install a switch to turn on my fans whenever I want to so I can lower the temp or via tuner change the ecm parameters to make the fans come on sooner. Can someone help with either?
Safety Car
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From: LeClaire Iowa
Drifting
Joined: Nov 2018
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From: Mays Landing, NJ
Drifting
Joined: Jul 2004
Posts: 1,353
Likes: 291
From: MA
Thread Starter
Intermediate
Joined: Aug 2025
Posts: 32
Likes: 8
From: Wilsonville, Oregon
Since it is a 1996 with OBD2 you could install a manual switch but you will probably cause a service engine soon light. I bought the JET DST used many many years ago. The JET DST will allow you to reprogram the engine computer for all different types of parameters including fan turn on temperatures. If you are ever going to modify your car it is a worthwhile investment.
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Drifting
Joined: Jul 2004
Posts: 1,353
Likes: 291
From: MA
I have an old netbook computer that I installed Windows XP on. I do not allow it to connect to the internet so it will not be vulnerable to any viruses.
Windows XP is the only safe and reliable way of using the JET DST. Even though in the instructions it says it can run on Win10, don't try it as it will eventually brick your PCM.
Drifting
Joined: Jul 2004
Posts: 1,353
Likes: 291
From: MA
If you only want to change your fan settings you could try to search for a used Hypertech Power Programmer. That has a setting to turn on the cooling fans earlier than stock and is simpler to use.
But be careful, if the Hypertech programmer was previously used on another vehicle the Hypertech will not work on a second vehicle unless the user of the first vehicle returned the original program back to the Hypertech.
But be careful, if the Hypertech programmer was previously used on another vehicle the Hypertech will not work on a second vehicle unless the user of the first vehicle returned the original program back to the Hypertech.
Instructor
Joined: Apr 2012
Posts: 186
Likes: 123
From: NJ
2025 Corvette of the Year Finalist - Modified
2024 C4 of the Year Winner - Modified
Don't bother using the JET DST. There's a better tuning option available for '96 OBD2 Corvettes:
https://lt-flash.com/product/lt-complete/
LT-FLASH will allow you to tune your PCM using free software like TunerPro, and it corrects the problems the JET DST has - minimizes the chances of bricking your PCM, and you can run everything on a modern laptop. They just released a software update that significantly speeds up the flashing process as well. Customer service is great.
I've used LT-FLASH and TunerPro to lower the cooling fan temps and disable skip-shift on my '96.
https://lt-flash.com/product/lt-complete/
LT-FLASH will allow you to tune your PCM using free software like TunerPro, and it corrects the problems the JET DST has - minimizes the chances of bricking your PCM, and you can run everything on a modern laptop. They just released a software update that significantly speeds up the flashing process as well. Customer service is great.
I've used LT-FLASH and TunerPro to lower the cooling fan temps and disable skip-shift on my '96.
Drifting
Joined: Jul 2004
Posts: 1,353
Likes: 291
From: MA
Don't bother using the JET DST. There's a better tuning option available for '96 OBD2 Corvettes:
https://lt-flash.com/product/lt-complete/
LT-FLASH will allow you to tune your PCM using free software like TunerPro, and it corrects the problems the JET DST has - minimizes the chances of bricking your PCM, and you can run everything on a modern laptop. They just released a software update that significantly speeds up the flashing process as well. Customer service is great.
I've used LT-FLASH and TunerPro to lower the cooling fan temps and disable skip-shift on my '96.
https://lt-flash.com/product/lt-complete/
LT-FLASH will allow you to tune your PCM using free software like TunerPro, and it corrects the problems the JET DST has - minimizes the chances of bricking your PCM, and you can run everything on a modern laptop. They just released a software update that significantly speeds up the flashing process as well. Customer service is great.
I've used LT-FLASH and TunerPro to lower the cooling fan temps and disable skip-shift on my '96.
Thread Starter
Intermediate
Joined: Aug 2025
Posts: 32
Likes: 8
From: Wilsonville, Oregon
Don't bother using the JET DST. There's a better tuning option available for '96 OBD2 Corvettes:
https://lt-flash.com/product/lt-complete/
LT-FLASH will allow you to tune your PCM using free software like TunerPro, and it corrects the problems the JET DST has - minimizes the chances of bricking your PCM, and you can run everything on a modern laptop. They just released a software update that significantly speeds up the flashing process as well. Customer service is great.
I've used LT-FLASH and TunerPro to lower the cooling fan temps and disable skip-shift on my '96.
https://lt-flash.com/product/lt-complete/
LT-FLASH will allow you to tune your PCM using free software like TunerPro, and it corrects the problems the JET DST has - minimizes the chances of bricking your PCM, and you can run everything on a modern laptop. They just released a software update that significantly speeds up the flashing process as well. Customer service is great.
I've used LT-FLASH and TunerPro to lower the cooling fan temps and disable skip-shift on my '96.
thank you for the info!
Instructor
Joined: Apr 2012
Posts: 186
Likes: 123
From: NJ
2025 Corvette of the Year Finalist - Modified
2024 C4 of the Year Winner - Modified
Speaking from personal experience, the LT-Unbrick works exactly as advertised.
Thread Starter
Intermediate
Joined: Aug 2025
Posts: 32
Likes: 8
From: Wilsonville, Oregon
Yes. That gets you the flash tool and the LT-Unbrick kit, which can fix a bricked PCM. The LT-Flash software is free on their website, and the TunerPro software you'll use to actually edit the PCM's .bin file is also free.
Speaking from personal experience, the LT-Unbrick works exactly as advertised.
Speaking from personal experience, the LT-Unbrick works exactly as advertised.
Instructor
Joined: Apr 2012
Posts: 186
Likes: 123
From: NJ
2025 Corvette of the Year Finalist - Modified
2024 C4 of the Year Winner - Modified
Yes. Here's what I changed my settings to:
Fan 1 Low Speed: 185ºF/85.25ºC
Fan 1 High Speed: 205ºF/95.75ºC
Fan 2 Low Speed: 205ºF/95.75ºC
Fan 2 High Speed: 212ºF/100.25ºC
Fan Low Speed Hysteresis: 6ºC
Fan High Speed Hysteresis: 4.5ºC
Fan 1 Low Speed: 185ºF/85.25ºC
Fan 1 High Speed: 205ºF/95.75ºC
Fan 2 Low Speed: 205ºF/95.75ºC
Fan 2 High Speed: 212ºF/100.25ºC
Fan Low Speed Hysteresis: 6ºC
Fan High Speed Hysteresis: 4.5ºC
New Guy
Joined: May 2020
Posts: 14
Likes: 6
From: IL
Better Radiator?
Agree the best approach is the address the problem (age, capacity) and the need for changing the fan triggering temps becomes less of an issue. That said, nothing wrong with wanting to tweak things like fan switching. Just keep in mind the switching temperature threshold is intentional, to allow oil temperature to reach a temperature that rids the oil of water caused by condensation
Start with making sure the area feeding the radiator is intact. The chin spoiler lip is critically important here since our cars are “bottom feeders” that are dependent on the cooling air being directed upward into the mouth under the nose of the car. If the chin is all wonky, the air isn’t being directed upward into into the mouth.
Then make sure the radiator itself is clean. It’s shocking how much debris gets trapped in there and blocks flow thru the radiator fins
Laslty, consider a replacement radiator like a Dewitts brand. The original radiator is pretty meager and begs for increased thermal capacity. Especially if its original and is clogged inside & out from 30 years of use
Start with making sure the area feeding the radiator is intact. The chin spoiler lip is critically important here since our cars are “bottom feeders” that are dependent on the cooling air being directed upward into the mouth under the nose of the car. If the chin is all wonky, the air isn’t being directed upward into into the mouth.
Then make sure the radiator itself is clean. It’s shocking how much debris gets trapped in there and blocks flow thru the radiator fins
Laslty, consider a replacement radiator like a Dewitts brand. The original radiator is pretty meager and begs for increased thermal capacity. Especially if its original and is clogged inside & out from 30 years of use
Melting Slicks
Joined: Nov 2016
Posts: 2,253
Likes: 3,074
From: So Cal
2023 C4 of the Year Finalist - Unmodified
Both fans run at either low speed or high speed. "Fan 1" is low speed. "Fan 2" is high speed. In the above, you do not mention "off" or "on". "Fan 1" and "Fan 2" do not have both "low speed" and "high speed".
Here's my interpretation of what skorpion317 wrote/has as fan operation paramaters:
Fan 1 (Low Speed) ON: 205ºF/95.75ºC
Fan 1 (Low Speed) OFF: 185ºF/85.25ºC
Fan 2 (High Speed) ON: 212ºF/100.25ºC
Fan 2 (High Speed) OFF: 205ºF/95.75ºC
Note that Fan 2 OFF is the same value as Fan 1 ON. Fan 2 OFF should probably be a couple of degrees F lower than Fan 1 ON so that if Fan 1 (Low speed) can not keep the temp below 205F, the fans won't cycle between the speeds at 205F. ("Hysteresis" possibly solves this, but I am not familiar with that parameter.) Cheers.
Last edited by IHBD; Apr 27, 2026 at 01:13 AM.
Thread Starter
Intermediate
Joined: Aug 2025
Posts: 32
Likes: 8
From: Wilsonville, Oregon
Just to clarify:
Both fans run at either low speed or high speed. "Fan 1" is low speed. "Fan 2" is high speed. In the above, you do not mention "off" or "on". "Fan 1" and "Fan 2" do not have both "low speed" and "high speed".
Here's my interpretation of what skorpion317 wrote/has as fan operation paramaters:
Fan 1 (Low Speed) ON: 205ºF/95.75ºC
Fan 1 (Low Speed) OFF: 185ºF/85.25ºC
Fan 2 (High Speed) ON: 212ºF/100.25ºC
Fan 2 (High Speed) OFF: 205ºF/95.75ºC
Note that Fan 2 OFF is the same value as Fan 1 ON. Fan 2 OFF should probably be a couple of degrees F lower than Fan 1 ON so that if Fan 1 (Low speed) can not keep the temp below 205F, the fans won't cycle between the speeds at 205F. ("Hysteresis" possibly solves this, but I am not familiar with that parameter.) Cheers.
Both fans run at either low speed or high speed. "Fan 1" is low speed. "Fan 2" is high speed. In the above, you do not mention "off" or "on". "Fan 1" and "Fan 2" do not have both "low speed" and "high speed".
Here's my interpretation of what skorpion317 wrote/has as fan operation paramaters:
Fan 1 (Low Speed) ON: 205ºF/95.75ºC
Fan 1 (Low Speed) OFF: 185ºF/85.25ºC
Fan 2 (High Speed) ON: 212ºF/100.25ºC
Fan 2 (High Speed) OFF: 205ºF/95.75ºC
Note that Fan 2 OFF is the same value as Fan 1 ON. Fan 2 OFF should probably be a couple of degrees F lower than Fan 1 ON so that if Fan 1 (Low speed) can not keep the temp below 205F, the fans won't cycle between the speeds at 205F. ("Hysteresis" possibly solves this, but I am not familiar with that parameter.) Cheers.
lt-flash.com - the complete kit
I assume this should work?
Instructor
Joined: Apr 2012
Posts: 186
Likes: 123
From: NJ
2025 Corvette of the Year Finalist - Modified
2024 C4 of the Year Winner - Modified
Just to clarify:
Both fans run at either low speed or high speed. "Fan 1" is low speed. "Fan 2" is high speed. In the above, you do not mention "off" or "on". "Fan 1" and "Fan 2" do not have both "low speed" and "high speed".
Here's my interpretation of what skorpion317 wrote/has as fan operation paramaters:
Fan 1 (Low Speed) ON: 205ºF/95.75ºC
Fan 1 (Low Speed) OFF: 185ºF/85.25ºC
Fan 2 (High Speed) ON: 212ºF/100.25ºC
Fan 2 (High Speed) OFF: 205ºF/95.75ºC
Note that Fan 2 OFF is the same value as Fan 1 ON. Fan 2 OFF should probably be a couple of degrees F lower than Fan 1 ON so that if Fan 1 (Low speed) can not keep the temp below 205F, the fans won't cycle between the speeds at 205F. ("Hysteresis" possibly solves this, but I am not familiar with that parameter.) Cheers.
Both fans run at either low speed or high speed. "Fan 1" is low speed. "Fan 2" is high speed. In the above, you do not mention "off" or "on". "Fan 1" and "Fan 2" do not have both "low speed" and "high speed".
Here's my interpretation of what skorpion317 wrote/has as fan operation paramaters:
Fan 1 (Low Speed) ON: 205ºF/95.75ºC
Fan 1 (Low Speed) OFF: 185ºF/85.25ºC
Fan 2 (High Speed) ON: 212ºF/100.25ºC
Fan 2 (High Speed) OFF: 205ºF/95.75ºC
Note that Fan 2 OFF is the same value as Fan 1 ON. Fan 2 OFF should probably be a couple of degrees F lower than Fan 1 ON so that if Fan 1 (Low speed) can not keep the temp below 205F, the fans won't cycle between the speeds at 205F. ("Hysteresis" possibly solves this, but I am not familiar with that parameter.) Cheers.
Hysteresis is the difference in coolant temperature needed to turn the fan off. So if Fan 1 low speed kicks on at 85ºC, and hysteresis is set at 6ºC, the fan will turn off when the coolant temp hits 79ºC.